Method and apparatus for determining a corrected monitoring voltage

ABSTRACT

A method and apparatus for correcting a locally measured inverter voltage. In one embodiment, the method comprises determining a voltage compensation to compensate for a voltage drop along an AC bus between an inverter and a remotely located point on the AC bus; obtaining a voltage measurement at the inverter; applying the voltage compensation to the voltage measurement to determine a corrected voltage measurement; comparing the corrected voltage measurement to a voltage requirement; and performing a corrective action at the inverter when the corrected voltage measurement does not meet the voltage requirement.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present invention is a continuation of co-pending U.S. patentapplication Ser. No. 12/701,262, filed Feb. 5, 2010, which claimsbenefit of U.S. provisional patent application Ser. No. 61/206,891,filed Feb. 5, 2009. Each of the aforementioned patent applications isherein incorporated in its entirety by reference.

BACKGROUND OF THE INVENTION

Field of the Invention

Embodiments of the present disclosure generally relate to power systemsand, more particularly, to a method and apparatus for determining acorrected monitoring voltage.

Description of the Related Art

Solar panels have historically been deployed in mostly remoteapplications, such as remote cabins in the wilderness or satellites,where commercial power was not available. Due to the high cost ofinstallation, solar panels were not an economical choice for generatingpower unless no other power options were available. However, theworldwide growth of energy demand is leading to a durable increase inenergy cost. In addition, it is now well established that the fossilenergy reserves currently being used to generate electricity are rapidlybeing depleted. These growing impediments to conventional commercialpower generation make solar panels a more attractive option to pursue.

Solar panels, or photovoltaic (PV) modules, convert energy from sunlightreceived into direct current (DC). The PV modules cannot store theelectrical energy they produce, so the energy must either be dispersedto an energy storage system, such as a battery or pumpedhydroelectricity storage, or dispersed by a load. One option to use theenergy produced is to employ one or more inverters to convert the DCcurrent into an alternating current (AC) and couple the AC current tothe commercial power grid. The power produced by such a distributedgeneration (DG) system can then be sold to the commercial power company.

In order to mitigate potential safety hazards, a DG coupled to acommercial power grid must be operated in accordance with relevantregulatory requirements, such as IEEE-1547. As part of meeting theIEEE-1547 requirements, an inverter within a DG must be deactivatedunder certain circumstances, including line frequency or line voltageoperating outside of pre-defined limits. The IEEE-1547 standardspecifies that such voltage requirements must be met at a Point ofCommon Coupling (PCC) between the commercial power system and the DG(i.e., a point of demarcation between the public utility service and theDG).

For installations where an inverter within a DG is located a significantdistance from the PCC, an output voltage measured at the inverter may behigher than a voltage measured at the PCC due a voltage drop along theline from the inverter to the PCC. In some circumstances, the measuredvoltage at the inverter may exceed the required voltage range althoughthe voltage at the PCC remains within the required range, resulting inthe inverter unnecessarily shutting down and thereby reducing energyproduction. Additionally, as the inverter ceases power production andthe voltage at the inverter is reduced to acceptable levels, theinverter once again activates and begins producing power, resulting in acontinued oscillation that negatively impacts power production.

Therefore, there is a need for a method and apparatus for correcting amonitoring voltage measured at an inverter.

SUMMARY OF THE INVENTION

Method and apparatus for correcting a locally measured inverter voltagesubstantially as shown and/or described in connection with at least oneof the figures, as set forth more completely in the claims.

Various advantages, aspects and novel features of the presentdisclosure, as well as details of an illustrated embodiment thereof,will be more fully understood from the following description anddrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above recited features of the presentinvention can be understood in detail, a more particular description ofthe invention, briefly summarized above, may be had by reference toembodiments, some of which are illustrated in the appended drawings. Itis to be noted, however, that the appended drawings illustrate onlytypical embodiments of this invention and are therefore not to beconsidered limiting of its scope, for the invention may admit to otherequally effective embodiments.

FIG. 1 is a block diagram of a system for distributed generation (DG) inaccordance with one or more embodiments of the present invention;

FIG. 2 is a block diagram of a control module in accordance with one ormore embodiments of the present invention;

FIG. 3 is a block diagram of an inverter in accordance with one or moreembodiments of the present invention; and

FIG. 4 is a flow diagram of a method for determining a correctedmonitoring voltage in accordance with one or more embodiments of thepresent invention.

DETAILED DESCRIPTION

FIG. 1 is a block diagram of a system 100 for distributed generation(DG) in accordance with one or more embodiments of the presentinvention. This diagram only portrays one variation of the myriad ofpossible system configurations. The present invention can function in avariety of distributed power generation environments and systems.

The system 100 comprises a plurality of inverters 102 ₁, 102 ₂ . . . 102_(n), collectively referred to as inverters 102, a plurality of PVmodules 104 ₁, 104 ₂ . . . 104 _(n), collectively referred to as PVmodules 104, an AC bus 106, and a load center 108.

Each inverter 102 ₁, 102 ₂ . . . 102 _(n) is coupled to a PV module 104₁, 104 ₂ . . . 104 _(n), respectively. In some embodiments, a DC-DCconverter may be coupled between each PV module 104 and each inverter102 (e.g., one converter per PV module 104). Alternatively, multiple PVmodules 104 may be coupled to a single inverter 102 (i.e., a centralizedinverter); in some such embodiments, a DC-DC converter may be coupledbetween the PV modules 104 and the centralized inverter.

The inverters 102 are coupled to the AC bus 106, which in turn iscoupled to the load center 108. The load center 108 houses connectionsbetween incoming power lines from a commercial power grid distributionsystem and the AC bus 106, and represents a Point of Common Coupling(PCC) between the system 100 and the commercial power grid. Theinverters 102 convert DC power generated by the PV modules 104 into ACpower, and meter out AC current that is in-phase with the AC commercialpower grid voltage. The system 100 couples the generated AC power to thecommercial power grid via the load center 108. Additionally oralternatively, the generated power may be coupled to appliances, and/orenergy generated may be stored for later use; for example, the generatedenergy may be stored utilizing batteries, heated water, hydro pumping,H₂O-to-hydrogen conversion, or the like. In some alternativeembodiments, the system 100 may comprise other types of renewable energygenerators in addition to or in place of the inverters 102, such as windturbines, hydroelectric systems, or the like.

The system 100 further comprises a control module 110 coupled to the ACbus 106. The control module 110 is capable of issuing command andcontrol signals to the inverters 102 in order to control thefunctionality of the inverters 102.

In accordance with one or more embodiments of the present invention,each of the inverters 102 applies voltage compensation to locallymeasured voltages (i.e., voltages measured at the inverter 102) whendetermining a monitored voltage for comparison to relevant voltageregulatory requirements. Such voltage compensation corrects for avoltage drop that occurs along the AC bus 106 between the inverters 102and the PCC and allows the inverters 102 to determine monitoring voltagelevels with respect to the PCC (i.e., corrected monitoring voltagelevels) for ensuring compliance with the relevant voltage regulatoryrequirements. In the event that a corrected monitoring voltage exceedsrequired limits, the corresponding inverter 102 may be deactivated or,alternatively, AC voltage regulation may be performed.

In some embodiments, the control module 110 may receive one or morevoltage samples (i.e., measurements) indicating a voltage proximate(i.e., at or near) the PCC. The control module 110 may then broadcastthese PCC voltage samples V_(pcc), to one or more inverters 102 fordetermining the corresponding corrected monitoring voltage as describedfurther below. The PCC voltage samples V_(pcc) may be obtained by ameasurement unit 112 deployed at or near the load center 108; in someembodiments, the measurement unit 112 and the control module 110 may bea single integrated unit. The measurement unit 112 may sample thevoltage proximate the PCC, for example, utilizing an analog to digital(ND) converter, and communicate the PCC voltage samples V_(pcc), to thecontrol module 110 for broadcast to the inverters 102. The measurementunit 112 may convert the voltage samples to a root mean square (RMS)value prior to transmission to the controller 110; alternatively, thecontroller 110 or the inverters 102 may perform such conversion. Oneexample of such a measurement unit may be found in commonly assignedU.S. patent application Ser. No. 12/657,447 entitled “Method andApparatus for Characterizing a Circuit Coupled to an AC Line” and filedJan. 21, 2010, which is herein incorporated in its entirety byreference.

In some embodiments, the measurement unit 112 may communicate the PCCvoltage samples V_(pcc), to the control module 110 utilizing power linecommunication (PLC), and the control module 110 may then broadcast thePCC voltage samples V_(pcc) to the inverters 102 utilizing PLC;alternatively, other wired and/or wireless communication techniques maybe utilized. In one or more alternative embodiments, the PCC voltagesamples V₃ may be obtained by the measurement unit 112 and communicateddirectly (i.e., without the use of the controller 110) to one or moreinverters 102 utilizing any of the communications techniques previouslymentioned.

In some alternative embodiments, the control module 110 may determinethe corrected monitoring voltage for one of more of the inverters 102,determine whether each corrected monitoring voltage is within requiredlimits, and/or initiate deactivation of one or more inverters 102 forwhich the corrected monitoring voltage levels exceed required limits.

FIG. 2 is a block diagram of a control module 110 in accordance with oneor more embodiments of the present invention. The control module 110comprises a communications transceiver 202 coupled to at least onecentral processing unit (CPU) 204. The CPU 204 is additionally coupledto support circuits 206, and a memory 208. The CPU 204 may comprise oneor more conventionally available microprocessors. Alternatively, the CPU204 may include one or more application specific integrated circuits(ASIC). The support circuits 206 are well known circuits used to promotefunctionality of the central processing unit. Such circuits include, butare not limited to, a cache, power supplies, clock circuits, buses,network cards, input/output (I/O) circuits, and the like.

The memory 208 may comprise random access memory, read only memory,removable disk memory, flash memory, and various combinations of thesetypes of memory. The memory 208 is sometimes referred to as main memoryand may, in part, be used as cache memory or buffer memory. The memory208 generally stores the operating system 214 of the control module 110.The operating system 214 may be one of a number of commerciallyavailable operating systems such as, but not limited to, SOLARIS fromSUN Microsystems, Inc., AIX from IBM Inc., HP-UX from Hewlett PackardCorporation, LINUX from Red Hat Software, Windows 2000 from MicrosoftCorporation, and the like.

The memory 208 may store various forms of application software, such asinverter control software 210 for operably controlling the inverters102. The communications transceiver 202 communicably couples the controlmodule 110 to the inverters 102 to facilitate command and control of theinverters 102. The communications transceiver 202 may utilize wirelessor wired communication techniques for such communication.

FIG. 3 is a block diagram of an inverter 102 in accordance with one ormore embodiments of the present invention. The inverter 102 comprises apower conversion module 302, a conversion control module 304, a voltagemonitoring module 306, an AC current sampler 308, and an AC voltagesampler 310.

The power conversion module 302 is coupled to the PV module 104 and actsto convert DC current from the PV module 104 to AC output current. Theconversion control module 304 is coupled to the AC voltage sampler 310for receiving an AC voltage reference signal from the commercial powergrid, and to the power conversion module 302 for providing operativecontrol and driving the power conversion module 302 to inject thegenerated AC output current in phase with the grid as required by therelevant standards.

The voltage monitoring module 306 is coupled to the conversion controlmodule 304, the AC current sampler 308, and the AC voltage sampler 310.The AC current sampler 308 is coupled to an output terminal of the powerconversion module 302, and the AC voltage sampler 310 is coupled acrossboth output terminals of the power conversion module 302. The AC currentsampler 308 and the AC voltage sampler 310 obtain samples (i.e.,measurements) of the AC inverter current and AC inverter voltage,respectively, at the output of the power conversion module 302 andprovide such inverter output current and voltage samples to the voltagemonitoring module 306. The AC current sampler 308 and the AC voltagesampler 310 may each comprise an A/D converter for obtaining theinverter output current and voltage samples, respectively. In some otherembodiments, rather than being directly measured, the inverter outputcurrent may be estimated based on DC input voltage and current to theinverter 102 and the AC voltage output from the inverter 102.

The voltage monitoring module 306 may be comprised of hardware,software, or a combination thereof, and comprises at least one CPU 314coupled to support circuits 316, memory 318, and a communicationstransceiver 324. The communications transceiver 324 is further coupledto at least one of the output lines from the power conversion module 302for communicating via PLC, for example, with the control module 110and/or the measurement unit 112. In alternative embodiments, thecommunications transceiver 324 may utilize wireless and/or other wiredcommunications techniques for such communication.

The CPU 314 may comprise one or more conventionally availablemicroprocessors. Alternatively, the CPU 314 may include one or moreapplication specific integrated circuits (ASIC). The support circuits316 are well known circuits used to promote functionality of the centralprocessing unit. Such circuits include, but are not limited to, a cache,power supplies, clock circuits, buses, network cards, input/output (I/O)circuits, and the like.

The memory 318 may comprise random access memory, read only memory,removable disk memory, flash memory, and various combinations of thesetypes of memory. The memory 318 is sometimes referred to as main memoryand may, in part, be used as cache memory or buffer memory. The memory318 generally stores the operating system (OS) 320 of the voltagemonitoring module 306. The OS 320 may be one of a number of commerciallyavailable OSs such as, but not limited to, Linux, Real-Time OperatingSystem (RTOS), and the like.

The memory 318 may store various forms of application software, such asvoltage monitoring module (VMM) software 322 for determining a correctedmonitoring voltage corresponding to the inverter 102.

To determine the corrected monitoring voltage, the voltage monitoringmodule 306 determines a correction coefficient K_(v) based on aninverter output voltage sample (i.e., a measurement of the inverteroutput voltage) received from the AC voltage sampler 310, and a PCCvoltage sample that indicates a measurement of a voltage proximate thePCC. In some embodiments, the PCC voltage sample is an RMS valueobtained by the measurement unit 112 and communicated from the controlmodule 110 as previously described. The voltage monitoring module 306determines the correction coefficient, K_(v), as follows:K _(v) =V _(pcc) /V _(meas)  (i)

where V_(pcc) is the PCC voltage sample and V_(meas) is the inverteroutput voltage sample.

Additionally, when K_(v) is computed, the voltage monitoring module 306computes an output power of the inverter, P_(meas). In some embodiments,the voltage monitoring module 306 utilizes the inverter output voltagesample V_(meas) and an inverter output current sample received from theAC current sampler 308, as well as phase angle, to determine the outputpower of the inverter, P_(meas). Alternatively, the voltage monitoringmodule 306 may calculate P_(meas) based on DC voltage and DC currentpertaining to the inverter 102 (for example, DC voltage and DC currentsamples obtained by the conversion control module 304) and a conversionefficiency of the inverter 102.

In some embodiments, the inverter 102 is pre-set with an initial K_(v)=1and determines a new K_(v) upon receiving a valid V_(pcc) measurementmessage. Such a message may be validated utilizing conventionalcommunication techniques, such as addressing and checksums (e.g., cyclicredundancy check, or CRC). If the new K_(v) is within an acceptablecorrection coefficient range, the voltage monitoring module 306 utilizesthe new K_(v) to determine a corrected monitoring voltage; if the newK_(v) is not within the acceptable correction coefficient range, K_(v)remains at its pre-set value until a next V_(pcc) is obtained. In someembodiments, the acceptable correction coefficient range is0.95<K_(v)<1.05.

The voltage monitoring module 306 utilizes K_(v) for computing thecorrected monitoring voltage V_(corr) upon obtaining inverter outputcurrent and voltage samples I_(inv) and V_(inv), respectively (e.g.,inverter output current and voltage samples obtained subsequent to thesamples utilized to compute K_(v)). The voltage monitoring module 306determines the corrected monitoring voltage V_(corr) as follows:V _(corr) =V _(inv)*(1−((P _(inv)*(1−K _(v)))/P _(meas)))  (ii)

where K_(v) is the correction coefficient, V_(inv) and P_(inv) are theinverter output voltage and power, respectively, and P_(meas) is theinverter output power determined at the time K_(v) was computed. P_(inv)is computed based on inverter output current and voltage samplesobtained by the AC current sampler 308 and the AC voltage sampler 310,respectively.

The voltage monitoring module 306 periodically computes V_(corr) basedon one or more of an updated inverter output power measurement P_(inv),an updated inverter output voltage measurement V_(inv) or an updatedK_(v) (e.g., K_(v) may be updated upon receiving a new valid V_(PCC)measurement message). In some embodiments, V_(corr) as well as allcorresponding voltage, current, power, and control parameters aredetermined at least once every line cycle (e.g., every 16.6667milliseconds). If a new valid V_(pcc) measurement message is notreceived within an aging time window, K_(v) is reset to “1” until avalid V_(pcc) message is received. In some embodiments, a linear agingfunction may be utilized; alternatively, a nonlinear aging function, ora combination of a linear and a nonlinear aging functions may beutilized.

In the event that the inverter output power P_(inv) moves outside of avalid output power range for the current K_(v), K_(v) is reset to “1”until a new valid V_(pcc) measurement message is received and a newK_(v) determined. The valid output power range may be some percentage ofthe rated total inverter power, for example, within the range of 5% to20% of the inverter power rating. In some embodiments, K_(v) may bereset to “1” in the event that the inverter output power P_(inv) exceedsa maximum power deviation.

The corrected monitoring voltage V_(corr) provides a more accurateestimate of the voltage at the PCC than the inverter output voltagealone for determining compliance with regulatory requirements pertainingto voltage levels at the PCC. In some embodiments, the voltagemonitoring module 306 determines whether the corrected monitoringvoltage V_(corr) is within a required voltage range with respect to theregulatory requirements; in the event the corrected monitoring voltageV_(corr) exceeds the required voltage range, the voltage monitoringmodule 306 provides a deactivation signal to the conversion controlmodule 304 to deactivate the power conversion module 302 or,alternatively, AC voltage regulation may be performed. In somealternative embodiments, one or more of determining the correctedmonitoring voltage V_(corr), determining compliance with regulatoryrequirements, and/or deactivation of one or more inverters as a resultof one or more corrected monitoring voltage levels exceeding a requiredvoltage range may be performed by the control module 110.

FIG. 4 is a flow diagram of a method 400 for determining a correctedmonitoring voltage in accordance with one or more embodiments of thepresent invention. In some embodiments, such as the embodiment describedbelow, AC current from a DG system comprising at least one DC-ACinverter is coupled to a commercial power grid at a PCC. Although theembodiment below is described with respect to a single inverter, eachinverter of the DG system may utilize the method 400. In alternativeembodiments, a controller for the DG system may utilize the method 400for determining one or more corrected monitoring voltages and/or drivingthe corresponding inverters accordingly.

The method 400 begins at step 402 and proceeds to step 404. At step 404,a correction coefficient K_(v) of an inverter has an initial value of“1”. In some embodiments, the inverter may be preset with K_(v)=1, forexample, at a factory during manufacturing. The method 400 proceeds tostep 406, where a voltage sample (i.e., measurement) indicating avoltage proximate the PCC (“V_(pcc)”), is obtained. The PCC voltagesample V_(pcc) may be received by the inverter as part of a validatedmessage transmitted to the inverter; for example, the message may bebroadcasted from a control module coupled to the DG system and validatedutilizing conventional communication techniques, such as addressing andchecksums (e.g., cyclic redundancy check, or CRC). In some embodiments,a data logger (e.g., the measurement unit 112 previously described) maybe coupled proximate the PCC, for example, at a load center coupling theDG system to the commercial power grid. The data logger may sample(i.e., measure) the voltage proximate the PCC, convert the voltagesample to an RMS value, and communicate the resulting PCC voltage sampleV_(pcc) to the controller for broadcast to the one or more inverters ofthe DG system. In some alternative embodiments, the PCC voltage sampleV_(pcc) may be converted to an RMS value at the controller or theinverter. In some other alternative embodiments, the data logger maydirectly communicate the PCC voltage sample V_(pcc) to the invertersutilizing wireless and/or wired communications techniques.

The method 400 proceeds to step 407, where a voltage sample of an ACoutput voltage of the inverter (V_(meas)) is obtained, for example, byan AC voltage sampler of the inverter. At step 408, a new K_(v) isdetermined as follows:K _(v) =V _(pcc) /V _(meas)  (iii)

Additionally, at the time K_(v) is computed, an output power of theinverter (P_(meas)) is determined based on V_(meas) and a sample of theAC output current from the inverter obtained, for example, by an ACcurrent sampler of the inverter.

At step 410, a determination is made whether K_(v) is within anacceptable correction coefficient range; in some embodiments, theacceptable correction coefficient range is 0.95<K_(v)<1.05. If it isdetermined that K_(v) is not within the acceptable correctioncoefficient range, the method 400 returns to step 404. If it isdetermined that K_(v) is within the acceptable correction coefficientrange, the method 400 proceeds to step 411.

At step 411, inverter output current and voltage samples are obtained(V_(inv) and I_(inv), respectively) and utilized to determine theinverter output power (P_(inv)). At step 412, a corrected monitoringvoltage is determined as follows:V _(corr) =V _(inv)*(1−((P _(inv)*(1−K _(v)))/P _(meas)))  (iv)

At step 414, a determination is made whether the corrected monitoringvoltage is within required regulatory limits. In some embodiments, theinverter may compare the corrected monitoring voltage to the regulatorylimits to make the determination; alternatively, the correctedmonitoring voltage may be communicated, for example to the controller orthe measurement unit, for determining compliance with the regulatorylimits. If the result of such determination is no, the method 400proceeds to step 422, where the inverter is deactivated; alternatively,AC voltage regulation may be performed. In some embodiments where theinverter is deactivated, upon determining that the corrected monitoringvoltage exceeds required limits, the inverter may cease powerproduction; alternatively, the inverter may receive a control signalfrom the controller or the measurement unit causing the inverter tocease power product. The method 400 then proceeds to step 424 where itends. If the result of the determination at step 414 is yes, the method400 proceeds to step 416.

At step 416, a determination is made whether a new valid V_(pcc)measurement message has been received. In some embodiments, V_(pcc) maybe determined and communicated to the inverter at least once every linecycle (e.g., every 16.6667 milliseconds). If a new valid V_(pcc)measurement message has been received, the method 400 returns to step407. If a new valid V_(pcc) measurement has not been received, themethod 400 proceeds to step 418. At step 418, a determination is madewhether an aging time window for K_(v) has been exceeded. In someembodiments, a linear aging function may be applied to K_(v) such thatK_(v) reaches a value of 1 at the end of the aging time window;alternatively, a nonlinear aging function, or a combination of linearand nonlinear aging functions, may be utilized. If the aging time windowhas been exceeded, the method 400 returns to step 404. If the aging timewindow has not been exceeded, the method 400 proceeds to step 419.

At step 419, inverter output current and voltage samples (V_(inv) andI_(inv), respectively) are obtained and utilized to determine a newinverter output power P_(inv). At step 420, a determination is madewhether the inverter output power P_(inv) is within a valid output powerrange for the current K_(v). The valid output power range may be somepercentage of the rated total inverter power, for example, within therange of 5% to 20% of the inverter power rating. If the inverter outputpower P_(inv) is within the valid output power range, the method 400returns to step 412. If the inverter output power exceeds the outputpower range, K_(v) is reset to 1 and the method 400 returns to step 404.

While the foregoing is directed to embodiments of the present invention,other and further embodiments of the invention may be devised withoutdeparting from the basic scope thereof, and the scope thereof isdetermined by the claims that follow.

The invention claimed is:
 1. A method for correcting a locally measured inverter voltage, comprising: determining a voltage compensation to compensate for a voltage drop that occurs along an AC bus based on the distance between an inverter and a remotely located point on the AC bus; obtaining a voltage measurement at the inverter; applying the voltage compensation to the voltage measurement to determine a corrected voltage measurement; comparing the corrected voltage measurement to a voltage requirement; and performing a corrective action at the inverter when the corrected voltage measurement does not meet the voltage requirement.
 2. The method of claim 1, wherein the corrective action is one of (i) deactivating the inverter or (ii) performing AC voltage regulation.
 3. The method of claim 1, wherein the voltage compensation is determined based on an initial power from the inverter, a subsequent power from the inverter, and a correction coefficient.
 4. The method of claim 3, wherein the correction coefficient is equal to a ratio of a voltage measurement obtained at the remotely located point and an initial voltage measurement at the inverter.
 5. The method of claim 4, wherein the initial voltage measurement is used to determine the initial power.
 6. The method of claim 1, wherein the remotely located point is a point of common coupling (PCC) between a commercial AC power grid and a distributed generator (DG) that comprises the inverter.
 7. The method of claim 6, wherein the DG is a photovoltaic (PV) system.
 8. An apparatus for correcting a locally measured inverter voltage, comprising: a voltage monitoring module comprising a central processing unit for: determining a voltage compensation to compensate for a voltage drop that occurs along an AC bus based on the distance between an inverter and a remotely located point on the AC bus; obtaining a voltage measurement at the inverter; applying the voltage compensation to the voltage measurement to determine a corrected voltage measurement; comparing the corrected voltage measurement to a voltage requirement; and performing a corrective action at the inverter when the corrected voltage measurement does not meet the voltage requirement.
 9. The apparatus of claim 8, wherein the corrective action is one of (i) deactivating the inverter or (ii) performing AC voltage regulation.
 10. The apparatus of claim 8, wherein the voltage compensation is determined based on an initial power from the inverter, a subsequent power from the inverter, and a correction coefficient.
 11. The apparatus of claim 10, wherein the correction coefficient is equal to a ratio of a voltage measurement obtained at the remotely located point and an initial voltage measurement at the inverter.
 12. The apparatus of claim 11, wherein the initial voltage measurement is used to determine the initial power.
 13. The apparatus of claim 8, wherein the remotely located point is a point of common coupling (PCC) between a commercial AC power grid and a distributed generator (DG) that comprises the inverter.
 14. The apparatus of claim 13, wherein the DG is a photovoltaic (PV) system.
 15. A system for correcting a locally measured inverter voltage, comprising: a plurality of photovoltaic (PV) modules; and a plurality of inverters coupled to the plurality of PV modules in a one-to-one correspondence, wherein each inverter of the plurality of inverters (i) determines a voltage compensation to compensate for a voltage drop along an AC bus between the inverter and a remotely located point on the AC bus; (ii) obtains a local voltage measurement; (iii) applies the voltage compensation to the local voltage measurement to determine a corrected voltage measurement; (iv) compares the corrected voltage measurement to a voltage requirement; and (v) performs a corrective action when the corrected voltage measurement does not meet the voltage requirement.
 16. The system of claim 15, wherein the corrective action is one of (i) deactivating the inverter or (ii) performing AC voltage regulation.
 17. The system of claim 15, wherein the voltage compensation is determined based on an initial power from the inverter, a subsequent power from the inverter, and a correction coefficient.
 18. The system of claim 17, wherein the correction coefficient is equal to a ratio of a voltage measurement obtained at the remotely located point and an initial voltage measurement at the inverter.
 19. The system of claim 18, wherein the initial voltage measurement is used to determine the initial power.
 20. The system of claim 18, wherein the remotely located point is a point of common coupling (PCC) between a commercial AC power grid and a distributed generator (DG) that comprises the plurality of PV modules and the plurality of inverters. 